Quality of service management for a wireless local area network

ABSTRACT

A method for managing quality of service (QoS) in a wireless local area network begins by receiving a traffic flow. The traffic flow is mapped to a traffic class (TC), based on QoS requirements of the traffic flow. A transmission budget of an access class (AC) is calculated, each AC including at least one TC. A determination is made whether the traffic flow can be admitted, by calculating whether the transmission budget can support the traffic flow. If the traffic flow is admitted, the parameters of the TC are adjusted and collisions in the TC between existing traffic flows and the newly admitted traffic flow are managed.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.10/981,002 filed on Nov. 4, 2004, which claims the benefit of U.S.Provisional Application No. 60/517,695, filed Nov. 5, 2003, which isincorporated by reference as if fully set forth herein.

FIELD OF INVENTION

The present invention relates to wireless local area networks (WLANs),and more particularly, to a method and system for managing quality ofservice (QoS) specifications in WLANs.

BACKGROUND

Wireless communication systems are well known in the art. Generally,such systems comprise communication stations, which transmit and receivewireless communication signals between each other. Depending upon thetype of system, communication stations typically are one of two types:base stations or wireless transmit/receive units (WTRUs), which includemobile units.

The term base station as used herein includes, but is not limited to, abase station, a Node B, a site controller, an access point (AP), orother interfacing device in a wireless environment that provides WTRUswith wireless access to a network with which the base station isassociated. In a WLAN, an AP is the preferred device, and will be usedherein to describe the present invention.

The term WTRU as used herein includes, but is not limited to, a userequipment, a mobile station, a fixed or mobile subscriber unit, a pager,or any other type of device capable of operating in a wirelessenvironment. WTRUs include personal communication devices, such asphones, video phones, and Internet ready phones that have networkconnections. In addition, WTRUs include portable personal computingdevices, such as PDAs and notebook computers with wireless modems thathave similar network capabilities. WTRUs that are portable or canotherwise change location are referred to as mobile units. In a WLAN, astation (STA) is the preferred device, and will be used herein todescribe the present invention.

A popular WLAN environment with one or more APs is built according toone of the IEEE 802.11 family of standards. The basic service set (BSS)is the basic building block of an 802.11 WLAN and consists of aplurality of STAs. A set of STAs which can talk to each other can form aBSS. Multiple BSSs are interconnected through an architecturalcomponent, called a distribution system (DS), to form an extendedservice set (ESS). An AP is a STA that provides access to the DS byproviding DS services and generally allows concurrent access to the DSby multiple STAs.

Systems compliant with the 802.11a/b/g WLAN standards are in widespreaduse. Quality of Service (QoS) capable WLANs are also emerging. The QoSsolutions/specifications vary between proprietary solutions andstandardized solutions where even the standard solutions have two typesof QoS schemes, namely: 802.11e enhanced distribution coordinationfunction (EDCA) and 802.11e hybrid coordination function (HCCA) schemes.

The 802.11e QoS facility defines a new hybrid coordination function(HCF) used only in a QoS enhanced basic service set (QBSS). HCF has twomodes of operation: HCF with contention operation (also known as EDCA)and HCF with polled access operation.

A basic concept utilized by these channel access functions is thetransmission opportunity (TXOP). A TXOP is a point in time when a STAcan begin transmitting frames for a given duration. During a TXOP, a STAcan transmit as many frames as possible in the TXOP, which is setaccording to the traffic class (TC) associated with the data.

A key difference between EDCA and HCCA is in how admission control ishandled. In EDCA, admission control is handled by a distributedadmission control (DAC) function, which measures the utilizationpercentage of the medium for each TC. The unused percentage of themedium is known as the available transmission budget for the TC. As thetransmission budget approaches zero, limitations are imposed on addingnew traffic flows or modifying existing traffic flows.

In HCCA, a STA requests particular reservation parameters for eachtraffic flow, based on the TC of the traffic flow. The HCF can thenreject, accept, or offer an alternative set of parameters to therequesting STA. While this is more robust than DAC, the traffic flowsneed to be properly scheduled.

SUMMARY

A method for managing quality of service (QoS) in a wireless local areanetwork begins by receiving a traffic flow. The traffic flow is mappedto a traffic class (TC), based on QoS requirements of the traffic flow.A transmission budget of an access class (AC) is calculated, each ACincluding at least one TC. A determination is made whether the trafficflow can be admitted, by calculating whether the transmission budget cansupport the traffic flow. If the traffic flow is admitted, theparameters of the TC are adjusted and collisions in the TC betweenexisting traffic flows and the newly admitted traffic flow are managed.

A method for managing quality of service in a wireless local areanetwork begins by receiving a traffic stream request, including atraffic specification (TSPEC) containing parameters of the trafficstream. The parameters contained in the TSPEC are analyzed and adetermination is made whether the traffic stream can be admitted. Thetraffic stream is admitted if it can be admitted without changing theparameters. The parameters are renegotiated if the traffic stream couldbe admitted by changing the parameters, and then the traffic stream isadmitted with the renegotiated parameters. The traffic stream isrejected if it could not be admitted.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding of the invention may be had from thefollowing description of a preferred embodiment, given by way ofexample, and to be understood in conjunction with the accompanyingdrawings wherein:

FIG. 1 is a block diagram of a QoS architecture in accordance with thepresent invention;

FIG. 2 is flowchart of a generic QoS procedure in accordance with thepresent invention;

FIG. 3 is flowchart of an EDCA-based QoS scheme in accordance with thepresent invention; and

FIG. 4 is flowchart of an HCF controlled channel access-based QoS schemein accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a general QoS architecture or component 100. Thearchitecture 100 is readily applicable to distributed coordinationfunction (DCF), enhanced distributed coordination function (EDCA), orhybrid coordination function (HCF) controlled channel access (HCCA)schemes. The architecture 100 includes a physical layer 102, a mediumaccess control (MAC) layer 104, and a network layer 106. The networklayer 106 includes QoS procedures such as traffic classifier, trafficshaping, scheduler, parameterization, admission control, trafficmonitoring/policing, and adaptation.

FIG. 2 illustrates a generic QoS procedure 200 for processingcommunication data for transmission. A traffic flow (i.e., at least onedata packet) is received from the higher layers (step 202). The trafficflow is classified into a traffic class (TC) according to the QoSrequirements for the particular type of communication data received(step 204).

In admission control, applications request specific resources from theAP, such as bandwidth and latency. Depending on the QoS requirements,network load, wireless medium conditions, and traffic flows, theserequests can be accepted or rejected by admission control (step 206).

Traffic shaping is used to control the traffic flow, so as to notoverload the channel (step 208). During traffic shaping, thetransmission of some data can be delayed and/or excess data can bedropped when a maximum data rate or amount is reached.

A scheduler determines when the data packets should be sent, bycontrolling the channel access of different traffic flows based on theirpriority and their QoS requirements (step 210).

A MAC parameterization process sets and dynamically adjusts the systemparameters based on QoS requirements. These parameters are set for eachTC and include a minimum contention window (CWmin) value, a maximumcontention window (CWmax) value, arbitrary interframe space (AIFS)value, a persistence factor (PF) value, and TXOP value (step 212). InEDCA, the contention window (CW) is expanded by the PF value after acollision. The PF value will determine if the CW has to be doubled,tripled, etc. after a collision.

The data packets are monitored and policed to control the traffic flow(step 214). Upstream packet inter-arrival time (from the packettimestamp) and downstream packet inter-dispatch time are monitored.Feedback for each flow is provided, such as the number of deadlinesmissed (how many times the data was delayed longer than the alloweddelay for a particular service type) and the delay variance (i.e.,jitter).

Adjustments to the system settings are made to adapt to changing networkconditions (step 216). During adaptation, depending on the feedbackobtained from the traffic monitoring function, the scheduler: changesits schedule; renegotiates the contract with higher layers, in which thescheduler can request the higher layer to reduce traffic, provide lessbandwidth for specific services, or admit fewer users; drops lowpriority traffic flows; or changes the parameters to adapt to thecurrent situation.

A feedback function provides feedback generated by the adaptationfunction to the other functions (step 218).

DCF-Based QoS Procedures

The generic outline described in connection with FIG. 2 can be readilyused for a DCF-based QoS algorithm and procedures. For the DCF case, alltraffic flows can be assumed to be equal. In order to ensure fairnessamong the traffic flows, the relative number of downlink accessopportunities per user can be controlled through scheduling. Differentconcepts of fairness may be applied. For instance, it is possible toattempt to ensure that all users have the same amount of downlinkbandwidth, that all users have an equivalent goodput (throughput withretransmissions), or that all packets have a similar queuing delay.

Although uplink scheduling cannot be directly controlled, for TCPtraffic it is possible for the AP to manipulate the uplink TCP ACKsprior to sending them to the distribution system. This allows someindirect control on the rate of uplink traffic an individual STAtransmits.

DCF can also implement a packet-discard function in traffic shaping,which is preferably consistent with the scheduling policy (e.g., discardpackets if user bandwidth is too high, if the packets have been queuedtoo long, or randomly). The maximum downlink bandwidth of a user can belimited by reducing the MAC scheduling opportunities during times ofcongestion. Downlink scheduling can be prioritized based on controllingthe queuing delay of packets.

Downlink bandwidth of users with high error rates can be limited. A linkwith high error rates means that there is a higher probability that thenext transmission will be in error (wasting bandwidth). An error alsomeans that the AP will have to increase its contention window, reducingaccess to the bandwidth.

During a DCF-based procedure, admission control is used to admit usersdepending on the available radio resources and link conditions. Afterusers are admitted, traffic shaping can be used to handle an overloadsituation by delaying traffic or by dropping packets. The scheduler isused to select which user sends the next packet based on many criteria,including fairness.

EDCA-Based QoS Procedures

FIG. 3 shows a high-level flowchart for an EDCA-based QoS procedure 300.A traffic flow (i.e., one or more data packets) is received from higherlayers (step 302). The traffic flow is mapped to the appropriate trafficclass (TC) based on its QoS requirements (step 304). Traffic flows arepreferably mapped to different TCs dynamically based on the QoSrequirements and previous observation windows for the networkperformance (i.e., channel quality and traffic load). The priority ofeach packet is checked, along with the current traffic load in thesystem, measurements for the last beacon interval, and networkconditions (step 306).

The purpose of QoS is to separate high-priority traffic fromlow-priority traffic. In a WLAN, it can be necessary to separate onehigh-priority traffic flow from another high-priority traffic flow inorder to avoid overloading the medium. Admission control is used forthis purpose by monitoring the available resources of the WLAN andmaking a determination whether to admit a new traffic flow.

In admission control (DAC with EDCA), a transmission budget is definedfor each access category (AC); each TC maps to an AC and an AC caninclude more than one TC. This scheme considers the delay and latencyrequirements for each class of QoS requirements (defined per AC) and thetransmission budget is adapted according to observed measurements for aprevious observation window, such as the number of deadlines missed,throughput, and delay variance. The transmission budget is also adjustedaccording to the feedback from the traffic monitoring/policingfunctions.

To determine if a traffic flow satisfies the admission criteria (step308), the transmission budget is evaluated. A traffic flow will only beadmitted if there are sufficient resources (i.e., if the transmissionbudget is large enough to support the traffic flow). The transmissionbudget per AC is equal to the maximum allowed transmission budget forthe AC minus the transmission budget already used by the AC.

If the admission criteria are satisfied (step 308), then the parametersfor the current traffic class are dynamically adjusted based on thelatest conditions and observed measurements (step 310). If the admissioncriteria are not satisfied, then the traffic flow is discarded orbuffered (step 312). Whether the traffic flow will be discarded orbuffered is based on its priority (e.g., the type or class of service).Higher priority traffic flows are buffered, while lower priority trafficflows are discarded. For example, if the traffic flow relates toemergency services data, it will be buffered, whereas if the trafficflow relates to normal background data, such as FTP data, the trafficflow will be discarded. If the traffic flow is buffered, then theprocedure 300 continues with step 308 as described above.

After the current traffic flow is admitted or discarded, the schedulermanages internal data collisions based on the priority of each trafficflow and dynamically adjusts the parameters for each TC according to thetraffic monitoring reports (step 314). The procedure then terminates(step 316).

HCF Controlled Channel Access-Based QoS Procedures (HCCA)

FIG. 4 shows an HCF controlled channel access (HCCA)-based QoS procedure400. The procedure 400 begins by receiving a request to add or modify atraffic stream (step 402). The request includes reservation parametersfor the traffic stream in a TSPEC associated with the traffic stream.The available channel capacity, link conditions, retransmission limits,priority, and QoS requirements of the TSPEC are checked (step 404).Scheduling parameters, such as minimum and maximum service intervals andTXOP durations, are determined (step 406). A determination is then madewhether the traffic stream can be admitted at the required rate anddelay bounds (step 408). From the TSPEC parameters, the traffic streamrequirements are compared with the available transmission budget. If thetime needed to send the traffic stream during the beacon period is lessthan the available time required to meet the QoS requirements of thetraffic stream (i.e., if the transmission budget is large enough toaccommodate the traffic stream), then the added traffic stream will beadmitted.

If the traffic stream can not be admitted, then the traffic streamrequest is rejected (step 410) and the procedure terminates (step 412).

If the traffic stream could be partially admitted with lowerrequirements (step 408), then the TSPEC is modified by renegotiatingwith higher layers, which generally indicates that the traffic streamwill be admitted with an alternate data rate (step 414). While it ispossible to renegotiate other parameters with higher layers, the datarate is most frequently adjusted, to reduce the bandwidth allocated fora traffic stream.

If the traffic stream meets the admission criteria (step 408), then thetraffic stream is admitted and the traffic monitoring/policing andadaptation functions are invoked to provide feedback to the schedulerabout the system performance and can drop violating traffic streams(step 416). A violating traffic stream can result from: (1) too manyre-transmissions, which can waste the medium time; or (2) higher layerapplications sending more than the expected level of traffic, which cancause congestion. In the latter case, lower priority traffic streams canbe dropped to alleviate the congestion.

A service schedule is created or updated (step 418) and the procedureterminates (step 412). A service schedule directs how traffic isscheduled during each beacon period, including which traffic streamswill be sent during the beacon period. The service schedule ispreferably adapted based on the feedback from the traffic monitoring andthe observed measurements for previous observation window.

The foregoing description makes references to 802.11-type systems as anexample only and not as a limitation. Other variations and modificationsconsistent with the invention will be recognized by those of ordinaryskill in the art.

Although the features and elements of the present invention aredescribed in the preferred embodiments in particular combinations, eachfeature or element can be used alone (without the other features andelements of the preferred embodiments) or in various combinations withor without other features and elements of the present invention. Whilespecific embodiments of the present invention have been shown anddescribed, many modifications and variations could be made by oneskilled in the art without departing from the scope of the invention.The above description serves to illustrate and not limit the particularinvention in any way.

1. A communication station (CS) comprising a quality manager component(QM) configured for managing quality of service (QoS) in a wirelesslocal area network, including: the QM configured to receive a trafficflow; the QM configured to map the traffic flow to a traffic class (TC),based on QoS requirements of the traffic flow; the QM configured tocalculate a transmission budget of an access class category (AC), eachAC including at least one TC; the QM configured to determine whether thetraffic flow can be admitted, by calculating whether the transmissionbudget can support the traffic flow; the QM configured to adjustparameters of the TC if the traffic flow is admitted; and the QMconfigured to manage collisions in the TC between existing traffic flowsand the newly determined admitted traffic flow.
 2. The CS of claim 1,wherein the transmission budget is equal to a maximum allowedtransmission budget for an AC minus the transmission budget already usedby the AC.
 3. The CS of claim 1, further comprising: the QM configuredto determine a priority of the traffic flow.
 4. The CS of claim 3,comprising: the QM configured to discard the traffic flow if the trafficflow is not admitted and if its priority is low.
 5. The CS of claim 3,comprising: the QM configured to buffer the traffic flow if the trafficflow is not admitted and if its priority is high.